DESCRIPTION (applicant's abstract): A long history of studies have suggested that the rostral hypothalamus promotes sleep, while the caudal hypothalamus promotes waking. My research advisor recently identified neurons in the ventrolateral preoptic area (VLPO) that may subserve the rostral hypothalamic sleep-promoting role. These neurons send inhibitory projections to a caudal hypothalamic structure, the tuberomammillary nucleus (TMN). The role of the TMN is unclear, but we propose that it promotes waking, and that it in turn sends inhibitory projections to the VLPO, thus defining a circuit with mutual antagonism between sleep and wake-promoting structures. This model suggests that the sleep-wake state is defined by a pair of competing neural systems, and has implications for disorders of sleep-wake regulation such as narcolepsy.